An inkjet recording device, for example, is known as an image forming device such as a printer, facsimile, copier or a multiple function processing machine of the printer, facsimile, and copier. In the above-mentioned inkjet recording device, while a recording medium is conveyed, a liquid drop of recording liquid (hereinafter “ink drop”) is adhered to the recording medium by using a recording head (image forming part) having a liquid jet head configured to jet the liquid drop of the recording liquid, so that image forming such as recording or printing is performed. Hereinafter, the recording medium is called a paper or transferred material. However, there is no limitation of material for the paper or the transferred material.
In the meantime, in a case where an image is formed by an ink jet recording method, ink adheres to paper. Therefore, when an image is formed on the paper, moisture included in the ink causes the paper to stretch. This phenomenon is referred to as cockling.
Cockling causes paper waviness so that the distance between the nozzle of a recording head and a paper surface varies depending on the position on the paper surface. Cockling may worsen to such an extent that, in the worst case, the paper comes into contact with the nozzle surface of the recording head.
As a result, not only the nozzle surface of the recording head but also the paper itself may be contaminated so that image quality is degraded. In addition, due to cockling, a portion in the paper where the ink drop adheres may be shifted.
In the related art inkjet recording devices, feeding of the paper is performed by using two groups of rollers arranged one group at each end of a printing area. With this structure, however, it is difficult to obtain high feeding precision unless the printing sheet is firmly in contact with both of the groups of rollers.
However, recently, a larger image forming area has become required, and in order to increase the printing area, there is proposed an inkjet image recording device having only one group of rollers for feeding the printing sheet.
However, such a device makes it even more difficult to obtain high feeding precision. Specifically, with the printing sheet being in contact with the rollers at only one side, the printing sheet floats relative to the rollers sometimes, and a force for conveying the printing sheet cannot be obtained. Consequently, the feeding precision becomes low, and the image quality declines.
Therefore, inkjet recording devices are proposed to solve this problem in which, in order to maintain flatness of the printing sheet, a charged seamless belt is provided to hold the paper on the belt by an electrostatic force due to the charge, and the belt is rolled in this state to convey the paper. In this way, floating of the paper from the belt is preventable and good flatness can be obtained.
Meanwhile, in the inkjet recording device in which the printing sheet is fed while being held on the feeding belt by an electrostatic force, the flatness of the paper is directly related to flatness of the belt.
In addition, in the above-mentioned inkjet recording device of the related art, the feeding belt is tensioned by at least two rollers and the portion of the belt between the rollers corresponds to the printing area, that is, the area printed on by the inkjet head. This portion of the belt rumples easily, and oscillates in a direction perpendicular to the belt surface when the belt is rolled, causing declination of flatness of the belt.
Thus, since generally the flatness of the printing sheet is directly related to flatness of the belt, the distance between the recording head and the printing sheet changes, causing image quality to decline.
Japanese Laid-Open Patent Application Publication No. 2004-175494 discloses an image forming device where flatness of the plane surface of a conveyance belt in an area facing the recording head can be secured. In this image forming device, the conveyance belt for conveying the paper is tensioned between a conveying roller and a tension roller, a guide member for guiding the conveyance belt is mounted on a rear face side of the part of the conveyance belt corresponding to the printing area of the recording head, and the guide member is mounted projection to the recording head side with respect to a tangent line between the rollers.
However, as discussed in Japanese Laid-Open Patent Application Publication No. 2004-175494, in a case where a plane surface state of the conveyance belt is formed due to a guide member configured to guide from a rear surface side and the paper is conveyed in a state where the paper is electrostatically adhered, the paper is separated from the conveyance belt just downstream of the plane surface formed due to the guide member.
The inventors of the present invention examined the reason for this problem and found that the conveyance belt passing over the guide member is supported so that it is tilted downward and to the roller because the upper surface of the guide member is mounted to project to the recording head side with respect to the tangent line between the rollers for securing the flatness of the conveyance belt in the area facing the recording head. As a result of this, it is found that this problem is related to the paper being easily self-stripped.
Especially, in a case where the paper is adhered to the conveyance belt by the electrostatic force, if a head end of the paper is separated from the conveyance belt, the electrostatic force does not work and the paper may be immediately separated. In addition, since the moisture is not sufficiently dried at the time when the second surface of the paper is both-sides printed, the paper including a relatively large amount of the moisture such as when set-solid printing is applied, the attraction force between the paper and the conveyance belt becomes low so that self stripping may easily happen.
Furthermore, when the ink adheres to the paper adhered by the conveyance belt, the paper may expand due to the moisture so that the paper waviness in a direction crossing the conveyance direction may be generated. When the paper is separated from the conveyance belt at the downstream side of the guide member, the paper waviness reaches back to the guide member part so that the abrasion between the recording head and the paper may happen, in which case the image receives damage.